Gas generating composition with polyvinyl chloride binder

ABSTRACT

AN INFLATION SYSTEM COMPRISING A GAS GENERATOR AND AN INFLATABLE DEVICE WHEREIN THE GAS GENERATOR CONTAINS A GASGENERATING COMPOSITION WHICH PRODUCES COMBUSTION PRODUCTS FREE FROM CORROSIVE, TOXIC, OR INFLAMMABLE COMPONENTS. THE GAS-GENERATING COMPOSITION COMPRISES PLASTICIZER POLYVINYL CHLORIDE FUEL BINDER AND A MIXTURE OF INORGANIC OXIDIZING SALT AND HALOGEN-FREE ALKALI METAL SALT IN A STOICHIOMETRY SUFFICIENT AT THE LEAST TO TRANSFORM ALL CARBON, HYDROGEN, AND HALOGEN IN THE COMPOSITION TO CARBON DIOXIDE, WATER AND ALKALI METAL HALIDE.

March 27, 1973 5, SCHEFFEE 3,723,295

GAS GENERATING COMPOSITION WITH POLYVINYL CHLORIDE BINDER Filed May 7,1971 Q INFLATABLE DEV/CE D INVENTOR 905527 6. SCHEFFEE nited Statesatent 3,723,205 Patented Mar. 27, 1973 ABSTRACT OF THE DISCLOSURE Aninflation system comprising a gas generator and an inflatable devicewherein the gas generator contains a gasgenerating composition whichproduces combustion products free from corrosive, toxic, or inflammablecomponents. The gas-generating composition comprises plasticizedpolyvinyl chloride fuel binder and a mixture of inorganic oxidizing saltand halogen-free alkali metal salt in a stoichiometry suflicient at theleast to transform all car- 'bon, hydrogen, and halogen in thecomposition to carbon dioxide, water and alkali metal halide.

BACKGROUND OF THE INVENTION Many devices, such as a protective passiverestraint or crash bag used in automobiles, escape slide chutes, liferafts, and the like, are normally stored deflated and are inflated withgas at the time of need. Such devices are generally both stored and usedin close proximity to human beings and, therefore, must be designed witha high safety factor effective at all times.

Inflation is generally accomplished by means of a gas, such as air,nitrogen, CO helium, and the like stored under pressure and furtherpressurized and supplemented at the time of use by the addition of hightemperature combustion gas products produced by the burning of agas-generating composition. In some cases the inflation gases are solelyproduced by the gas-generating compositions.

It is obviously very important that the gas-generating composition becapable of safe and reliable storage without decomposition or ignitionat all temperatures likely to be encountered in the vehicle or otherstorage environment as, for example, up to temperatures as high as about220 F. It is also important that substantially all of the combustionproducts generated during use be non-toxic, non-corrosive, andnon-inflammable, particularly where the device is used in a closedenvironment such as an automobile.

Gas-generating compositions employed hitherto have not met all of theabove qualifications. Examples of compositions which have been usedinclude black powder and plasticized nitrocellulose (double base)propellant compositions. The double base propellants are unstable athigh ambient temperatures. Storage and use is generally restricted totemperatures below 140 F. Both black powder and double base propellantgenerate toxic and/ or inflammable gases. Double base propellantsproduce, in addition to carbon dioxide and Water, carbon monoxide andhydrogen, a mixture which is both toxic and inflammable. Black powderproduces carbon monoxide in toxic concentrations as well as beingrelatively inefficient in volume of gas generated. The use ofconventional composite propellants has also been suggested. Such propellants, however, have reactive components and stoichi ometries whichresult in toxic, corrosive, or flammable combustion products, which, inaddition to carbon monoxide and hydrogen, may include hydrogen chloride,alkali metal oxides or hydroxides, nitrogen oxides, and the like.

For the applications contemplated herein, it is also im portant to havegas-generating compositions which generate large volumes of gas, whichcan be stored without adverse degradation for periods as long as 5 to 10years and which can be mass produced at low cost.

The gas-generating compositions employed in the gasgenerator of theinflation system of this invention have important advantages whichresult in significantly improved inflation systems. These advantagesinclude inter alia:

(l) Storageability at ambient temperatures up to 220 F.

for as long as five to ten years.

(2) High autoignition temperature, very low impact sensitivity, and verylow friction sensitivity.

(3) Combustion products free from toxic, corrosive, and

flammable components.

(4) High volumetric gas-generating capability per unit Weight ofgas-generating composition.

(5) Capability for safe, reliable, low-cost, mass production.

SUMMARY OF THE INVENTION The invention is an improvement in conventionalinflation systems comprising a gas generator and an inflatable device.The inflatable device may be a bag designed to act as a passiverestraint to protect an automobile driver or passenger in case ofcollision, an aircraft escape chute, a life raft, and the like. The gasgenerator contains a gas-generating composition capable of producinggaseous combustion products which can be used to pressurize andsupplement a primary inflation gas source, such as air, nitrogen, carbondioxide, helium and the like, maintained under pressure in a separatestorage chamber or to inflate the inflatable device directly without anadditional gas supply.

The improvement comprises gas-generating compositions which consistessentially of plasticized polyvinyl chloride fuel binder containingdispersed therein an inorganic oxidizer selected from the groupconsisting of ammonium perchlorate, alkali metal chlorate orperchlorate, alkaline earth metal nitrate, and mixtures thereof,hereinafter called primary oxidizer, and halogen-free alkali metal saltreactive with the combined chlorine in the polyvinyl chloride (andammonium perchlorate if used as primary oxidizer) to form alkali metalchloride. The halogen-free alkali metal salt may also be an oxidizer inWhole or in part. Total oxidizer and halogen-free alkali metal salt arepresent in amount at least sufficient to oxidize all available carbon tocarbon dioxide and all available hydrogen to Water and to convert allavailable combined chlorine to the alkali metal halide. Oxidizer and/ oralkali metal salt in excess of these stoichiometric requirements may beemployed.

The invention also comprises a method for inflating inflatable deviceswith gaseous combustion products which are non-toxic, non-corrosive, andnon-flammable so that the devices can be safely employed in closeproximity to human beings, particularly in confined spaces. The methodcomprises burning the gas-generating composition aforedescribed andinjecting the gaseous combustion products into the inflatable deviceeither solely or as a pressurizing supplement to a separate pressurizedgas, such as air, nitrogen, carbon dioxide, or helium.

DRAWINGS The figure is a longitudinal sectional view partly in elevationof an inflation system utilizing a gas generator and an inflation devicein accordance with this invention.

DETAILED DESCRIPTION As aforedescribed, the improvement in the inflationsystem resides in loading the gas generator portion of the inflationsystem with a gas-generating composition comprising a plasticizedpolyvinyl chloride fuel binder containing dispersed therein an inorganicoxidizer salt selected from the group consisting of ammoniumperchlorate, alkali metal chlorate or perchlorate, alkaline earth metalnitrates, and mixtures thereof, and a halogen-free, alkali metal salt,total oxidizer and alkali metal salt being present in amount at leastsufficient to oxidize all avalaible carbon and hydrogen in thecomposition to carbon dioxide and water and to convert all availablecombined chlorine to the alkali metal halide.

The term polyvinyl chloride as employed herein includes both thehomopolymer and a copolymer containing up to about of a copolymerizedcomponent, such as vinyl acetate or vinylidene chloride. Preferably thepolyvinyl chloride is essentially fully polymerized and employed in theform of plastisol-grade spheroidal particles.

Any organic liquid plasticizer compatible with polyvinyl chloride may beemployed. Such plasticizers are wellknown in the art. Preferably, theplasticizer is of the type suitable for fiuid plastisol formation, as,for example, alkyl and alkoxyalkyl adipates, sebacates, and phthalates,e.g. dibutyl and dioctyl sebacate, dibutyl, dioctyl, and dimethoxyethylphtha ate, dibutyl dioctyl and di(3,5,5trimethylhexyl) adipate; glycolesters of higher fatty acids and the like. The plastisol-forminglasticizers are high boiling solvents for the polyvinyl chloride whichform fluid suspensions with the resin particles at ordinary temperaturesbecause of the low solubility at such temperatures and dissolve theresin at elevated temperatures to form a solid gel.

The preferred ratio of polyvinyl chloride to plasticizer is generallyfrom about 2 parts resin to 3 parts plasticizer to about 3 parts resinto about 2 parts lasticizer for desirable physical properties of thecured gasgenerating grains, such as tensile strength and minimum coldflow. In view of the high solids loadings generally required by theinflation system applications, the higher ratios of plasticizer to resinare desirable in order to maintain processability of the mix. For someinflation applications, physical property requirements are less exactingand the ratio of plasticizer to resin may be increased to as much as 2.5to 1 while maintaining adequate physical properties of the solidgas-generating grain for the application.

The fluid polyvinyl chloride-plasticizer slurries can accommodate up toas much as 90% of added solids if, as is well-known in the art, particlesizes of the added solids are properly selected and distributed, withoutloss of adequate fluidity to permit casting and curing withoutapplication of high pressures.

The polyvinyl chloride-plasticizer slurry loaded with oxidizer and suchother solids as may be required is cured simply by heating to thesolution temperature of the polyvinyl chloride in the plasticizer,generally about 160 to 175 C. Since the polyvinyl chloride is fullypolymerized, no potentially variable cure reaction occurs and theresulting cured gas-generating grains are highly reproducible andreliable. Polyvinyl chloride plastisol gas-generating propellants andprocess for making them are described in U.S. Pat. 2,966,403.

The loaded polyvinyl chloride-plasticizer plastisol slurries areparticularly amenable to curing and casting by extrusion as disclosed inU.S. Pat. 3,155,749. Briefly, the loaded slurry is introduced into anelongated extruder barrel through which it is advanced by a rotatingworm screW with simultaneous generation of frictional heat, whichtogether with heat supplied by means of a heating jacket provides theelevated temperature required for the solution cure. The mix is fullycured when it completes its passage through the extruder barrel thoughit is still in a sufliciently hot, soft state to be shaped by passagethrough a die after which the shaped extruding column is cooled and cutinto grains of the desired length. The extrusion process is continuousand provides rapid, low-cost mass production of the gas-generatinggrains.

Use of the specified primary inorganic oxidizer salts in combinationwith the halogen-free alkali metal salts in the amounts required by thespecified stoichiometry provides maximized non-toxic, non-corrosive,non-flammable gas production and neutralization of the chlorinecomponent in the polyvinyl chloride binder in the form of a non-toxicalkali metal chloride product. The primary oxidizers, in addition tooxygen, produce per se or by reaction with the halogen-free alkali metalsalt additive, only non-toxic, non-corrosive, and non-flammablecombustion products. The halogen-free alkali metal salt additiveprevents formation of corrosive HCl or chlorine.

The alkali metal, e.g. Na, K, Li, chlorates and perchlorates formnon-toxic alkali metal chlorides, with the remainder of the oxidizersalt molecules providing oxygen for combustion of the fuel. Of these,potassium perchlorate is generally preferred. Ammonium perchlorate ishighly useful as an oxidizer because it increases gas production in theform of nitrogen and water and reduces the percentage of solid products.It also provides somewhat lower flame temperatures than thecorresponding alkali metal salts. The HCl produced by ammoniumperchlorate as a decomposition product is corrosive and must beneutralized by transformation into the alkali metal chloride. Thus,sufficient halogen-free alkali metal salt must be incorporated for thispurpose as well as for the neutralization of the HCl decompositionproduct of the polyvinyl chloride resin binder.

The alkaline earth metal nitrate oxidizer salts, such as Ba(NO or Sr(NOdecompose to form highly stable non-toxic oxides as combustion productsand thus can be safely and efficiently used as oxidizers ingas-generating compositions. Since burning rates obtained with theseoxidizers are generally lower than those obtained with the ammonium oralkali metal chlorates, perchlorates, or nitrates, it is generallypreferred to employ the alkaline earth metal nitrate oxidizer inadmixture with one of the foregoing oxidizers.

The halogen-free alkali metal salts, as aforementioned, may be anycompound which reacts with the chlorine in the polyvinyl chloride and inany ammonium perchlorate used as primary oxidizer to form a non-toxicalkali metal salt. The alkali metal moiety can be, for example, Na, K,or Li. Preferably, though not essentially, the alkali metal salt is alsoan oxidizer, thereby supplementing the gasforming oxidizing action ofthe primary oxidizer and contributing to the desired carbon dioxide andWater stoichiometry. Preferred halogen-free alkali metal oxidizers arethe nitrates, e.g. NaNO and KNO since they have the additional advantageof forming nitrogen gas as a combustion product and of conferring goodcombustion properties, such as desired burning rate and pressureexponent. Other alkali metal oxidizers include, for example, the alkalimetal nitrites.

Alkali metal salts which do not react as oxidizers may also be used.Preferably they contribute non-toxic, gaseous decomposition productswhich increase total gas production, decrease concentration of solidcombustion products and act as coolants. Examples of suitablenon-oxidizer salts include, but are not limited to, alkali metaloxalates, e.g. Na C O K O O carbonates and bicarbonates, e.g. K CO Na CONat-K10 azides, e.g. KN and the like.

As aforementioned the total amount of oxidizer, in cluding primaryoxidizer and halogen-free alkali metal oxidizer, should be at leastsuflicient to oxidizer all available carbon and hydrogen present in thecomposition to carbon dioxide and water. Excess primary oxidizer may beemployed and is, in fact, advantageous since its endothermicdecomposition contributes to gas formation in the form of free oxygenand to reducing flame temperature, thereby functioning as a coolant. Theamount of halogen-free alkali salt should be in amount at leastsuflicient to transform all available halogen to the alkali metalhalide. By available halogen is meant halogen not already combined withalkali metal as in the case of an alkali metal chlorate or perchlorate.The halogen-free alkali metal salt should not be included in substantialexcess. The total amount of available alkali metal should not exceedavailable halogen by more than about 10 mol percent. Althoughstoichiomet'ric proportions of alkali metal and halogen are preferred,in some cases a small excess of alkali metal may be desirable to ensurecomplete freedom from HCl or C1 formation since these are considerablymore toxic than small amounts of alkali metal oxide or hydroxide.

The particular amounts and relative proportions of primary oxidizer andhalogen-free alkali metal salt will obviously vary with the particularbinder concentration, the particular plasticizer, and the particularprimary oxidizer and halogen-free alkali metal salt employed. They can,however, be readily calculated in accordance with well-known proceduresby anyone skilled in the art.

In addition to the components aforedescrbed, othzr conventionaladditives may be incorporated into the gasgenerating compositions. Theyinclude, for example, stabilizers for the polyvinyl chloride, burningrate catalysts, coolants and the like.

The plasticized polyvinyl chloride resin binder gasgeneratingcompositions are very stable and can be stored at temperatures as low as50 F. and as high as 220 F. without adverse degradation for periods aslong as five to ten years. Ignition temperatures are very high andsensitivity to impact, friction and electrostatic charge is very low sothat the gas generators containing the compositions can be stored safelyin con-fined spaces in close proximity to human beings. Otheradvantageous properties include high densities thereby reducing chambersize requirements, easy ignition, high burning rates, and inexpensiveraw material requirements.

The figure shows schematically, an inflation system utilizing theimprovement of this invention. Pressure vessel 1 contains a gas, such asair, under pressure. Gas generator 2 seated within the pressure vesselcomprises a combustion chamber 3 equipped with a restricted aperture ornozzle 4 and containing a shaped gas-generating grain 5 of compositionas aforedescribed. Electrically actuated squib 6 is employed to ignitethe gas-generating grain. The gas generator is sealed with rupturablecap 7. The pressure chamber is provided with outlet means 8 sealed withrupturable disc 9 and connected by conduit 10 to inflatable device 11.Safety valve 12 is designed to preclude development of excessivepressures in the pressure vessel.

In operation, the gas-generating grain is ignited. When adequatepressure has developed within the gas-generator, seal 7 ruptures and thehot high pressure combustion gases generated by the burning grain ventinto the pressurized gas, e.g. air, in the pressure chamber. The airpressure is considerably increased both by the heat and added volume ofthe combustion gases. Seal 9 ruptures and the high pressure mixture ofair and combustion gases pour into and inflate the inflatable device.The compressed air acts as a heat sink to reduce the temperature of hotcombustion gases to a safe level.

In some applications, the pressure chamber contaning compressed air orother gas can be dispensed with and the inflatable device connecteddirectly to the gas generator. Temperature reduction of the hotcombustion gases can be accomplished by adding coolant compounds to thegas-generating compositions and by storing a vaporizable liquid, such aswater, in the inflatable device.

The gas-generating compositions described in the following examples wereprocessed into shaped grains by mixing the plastisol grade polyvinylchloride with the plasticizers, primary oxidizer, halogen-free alkalimetal salt, and other additives, such as stabilizers and burning ratecatalyst in a conventional mixer. The viscous but still fluid mixtureswere then either poured into molds and heated to the fusion temperatureof the polyvinyl chloride in the plasticizer or solution-cured bycontinuous passage through a heat-jacketed worm extruder barrel, afterwhich the extruding column was passed through a shaping die, cooled, andcut to desired lengths.

Ballistic properties:

Burning rate at 500 p.s.i.a., 70 F.: 0.60 in./sec.

Burning rate at 5000 p.s.i.a., 70 F.: 0.60 in./sec.

Burning rate pressure exponent n: 0.67 Safety data:

Autoignition temperature: 680 F. Impact sensitivity (12 tests negativewith 6 kg. at

50 cm.): 300 -kg.-cm.

Friction sensitivity (Esso Screw Friction Test (two screwloaded flatplates with propellant and No. carborundum grit between)): 300 in./1b.

Card-gap test (Tetryl pellet placed against propellant and detonatednopropellant detonation in 4 tests): zero cards EXAMPLE 2 Composition:Percent by weight Polyvinyl chloride 5.616 Dioctyl adipate 8.22.7Stabilizer 0.158 Carbon black 0.039 K010 55.820 Sr(NO 21.053 KNO 9.087

Burning rate at 1000 p.s.i.a., 70 F.: 0.89 in./sec. Burning rate at 4000p.s.i.a., 70 F.: 2.51 in./sec. Burning rate pressure exponent n: 0.75

EXAMPLE 3 Composition: Percent by weight Polyvinyl chloride 6.318Dioctyl adipate 9.477 Carbon black 0.048 Stabilizer 0.196 Ammoniumperchlorate 42.598 NaNO 39.407 F3203 Burning rate at 3000 p.s.i.a., 70R: 1.6 in./sec. Burning rate pressure exponent n: 0.63

EXAMPLE 4 Composition: Percent by weight Polyvinyl chloride 4.513Dibutyl sebacate 6.770 Stabilizer 0.135 Carbon black 0.034 Ammoniumperchlorate 29.032 NaNO 27.139 Sr(N-O 31.029 Fe O 1.348

Burning rate at 3000 p.s.i.a., 70 F.: 1.4 in./sec. Burning rate pressureexponent n: 0.70

Although this invention has been" described with reference toillustrative embodiments thereof, it will be apparent to those skilledin the art that the principles of this invention can be embodied inother forms but within the scope of the claims.

I claim:

1. A non-toxic, non-corrosive, and non-flammable combustiblegas-generating composition for use in inflating an inflatable devicecomprising:

plasticized polyvinyl chloride fuel binder,

inorganic oxidizer salt selected from the group consisting of ammoniumperchlorate, alkali metal chlorates and perchlorates, alkaline earthmetal nitrates and mixtures thereof,

halogen-free alkali metal salt reactive with available 8. Thecomposition of claim 2 wherein the inorganic halogen to form alkalimetal halide, oxidizer salt is ammonium perchlorate.

said composition containing total oxidizer in amount 9. The compositionof claim 3 wherein the inorganic at least suflicient to convert allavailable carbon to oxidizer salt is ammonium perchlorate. carbondioxide and all available hydrogen to water, 5

said composition containing available combined alkali References Citedmetal in amount at least sufiicient to convert all avail- UNITED STATESPATENTS able halogen to alkali metal halide up to a maximum 3,155,74911/1964 'Rossen et al 14976 X 82 22;: 10 ml Percent excess the avallable10 3,180,373 4/1965 Hebenstreit 141-4 2. The composition of claim 1wherein the halogen- 3107186 10/1963 Scurlock et 149-19 2,904,420 9/1959 Holker 1496l X free alkali metal salt is an alkali metal nitrate. 3066 479 12/1962 K h 149 35 X 3. The composition of claim 2 wherein thealkali metal 0c nitrate is sodium nitrate or potassium nitrate 33628591/1968 Sutton et a1 149*19 3,373,062 3/1968 Morris 14919 X 4. Thecomposition of claim 1 wherein the inorganic 15 oxidizer salt ispotassium perchlorate.

5. The composition of claim 2 wherein the inorganic CARL D QUARFORTHPrimar Examiner oxidizer salt is potassium perchlorate. y

3,692,495 9/1972 Schneiter et a1. 280-150 AB 6. The composition of claim3 wherein the inorganic E. A. MILLER, Assistant Examiner oxidizer saltis potassium perchlorate. 2O

7. The composition of claim 1 wherein the inorganic X- oxidizer salt isammonium perchlorate. 149 35, 61 76 AB

